FIG. 7 is a diagram for illustrating the schematic construction of a laser display 100 as one example of a conventional video projector.
The conventional laser display 100 shown in FIG. 7 comprises laser light sources 102, 104, 106 for generating red, green, and blue laser beams, lenses 107 for converting laser beams into parallel lights, integrators 108 for equalizing light intensity of the light that has transmitted through the lens 107, a LCD panel 110 for transmitting the light from the integrator 108, a control circuit 112 for controlling the LCD panel 110, a transmission light prism 109 for multiplexing the light that has transmitted through the LCD panel 110, and a projection lens 111 for projecting the light which has come from the transmission light prism 109 onto a screen 101.
The laser light sources 102, 104 are semiconductor lasers, and they irradiate a blue and a red laser beam, respectively. Further, the laser light source 106 includes a fiber laser 103 and an SHG element 105, and irradiates a green laser beam by wavelength converting near-infrared light having a wavelength in the vicinity of 1060 nm which is irradiated from the fiber laser 103 using the SHG element 105.
Next, the operation of the conventional laser display 100 will be described.
Three color lasers of red, green, and blue emitted from the respective laser light sources 102, 104, 106 are converted into parallel lights by using the lenses 107, and are equalized in light intensity by using the integrators 108, to transmit through the LCD panel. The transmitted lights are modulated according to RGB signals at the LCD panels, respectively.
The lights which have been transmitted through the corresponding LCD panel 110 are synthesized by using the transmission light prism 109, and are projected onto the screen 101 by using the projection lens 111.
In this way, a two-dimensional image is displayed on the screen 101.
In this conventional video projector, since the lights of the respective RGB light sources are monochrome lights, a displayable color range can be broadened relative to a projector which displays an image with an NTSC signal by using an appropriate laser light source, and thereby a display of vivid images with higher color purity becomes possible. Further, reduction in power consumption is realized as compared with a case where a lamp is used for a light source.
FIG. 8 is a diagram illustrating devices which can be connected to the above-described conventional laser display 100.
This conventional laser display 100 receives a video signal from its RGB terminals 200, and those which have output terminals for RGB signals, e.g., a personal computer 201 such as a notebook PC, a video game console 202, an optical disc player 201 such as various types of DVDs, an optical disc recorder 204 including one of a VTR integrated type, a camera integrated type VTR 205, a non-portable VTR 206, a BS/CS tuner 207, a TV 208, a hard disc recorder 209 including various optical disc drive integrated type ones, an Internet broadcasting STB (set top box) 210, a CATV STB 211, a digital terrestrial broadcasting STB 212, and a BS HDTV broadcasting STB 213.
In addition, in accordance with formats of signals outputted from a device which is connected to the laser display, a D4 input terminal, a DVI-D input terminal, an IEEE 1394 terminal, a component terminal, an S terminal, and a video terminal and the like may be provided.
Further, FIG. 9(a) is a diagram illustrating a detailed constitution of the fiber laser 103, FIG. 9(b) is a cross-sectional view of a tapered fiber, and FIG. 9(c) is a cross-sectional view of a rare-earth doped fiber.
The fiber laser 103 is constituted by a pump light source 116, a tapered fiber 117, a rare-earth doped fiber 118, a fiber Bragg grating (hereinafter referred to as “FBG”) 119, and a polarizer 121.
The FBG 119a which is formed at the laser beam incident side of the rare-earth doped fiber 118 has a reflectivity of about 100% against the reflected light from the output end facet. On the other hand, the FBG 119b which is formed at the laser beam output side is designed to have a reflectivity of approximately 10%.
Further, Yb (Ytterbium) is added to the rare-earth doped fiber 118, and this rare-earth doped fiber 118 is a kind of solid laser which has a function of converting the wavelength of a light from the pump light source 116 from 980 nm to 1060 nm, and absorbs a large amount of light having a wavelength of 980 nm.
Next, the operation of the fiber laser 103 will be explained.
A laser beam irradiated from the pump light source 116 is optically coupled to the rare-earth doped fiber 118 by using the tapered fiber 117. The oscillation wavelength of the pump light source 116 is 980 nm.
The wavelength of the laser beam coupled to the rare-earth doped fiber 118 is locked by the FBG 19.
The laser beam which is coupled to the rare-earth doped fiber 118 is absorbed in the rare-earth doped fiber 118, and is wavelength converted into a laser beam of a wavelength 1060 nm, and is outputted as a laser beam in the vicinity of 1060 nm. For an input light of 12 W, the output light is 8 W.
The outputted infrared light of 1060 nm is wavelength converted into a green light of a wavelength of 530 nm by the SHG(second harmonic generation) element 120. The output of the green light is 3 W.
In order to enhance the absorption of pump light in the rare-earth doped fiber 118, the length of the rare-earth doped fiber is important. That is, the rate of absorption of a pump light can be enhanced as the rare-earth doped fiber 118 is longer, and therefore a length of several meters is required. Accordingly, the rare-earth doped fiber is usually contained in a fiber laser containing box 103a in a circularly wound state (in a looped shape), as shown in FIG. 7.
Patent document 1: Japanese published patent 2003-98476 (page 4, FIG. 1)